Environmental Protection Agency Administrator Gina McCarthy debuted a draft proposal for carbon emissions limits set by the agency for new power plants in September. But the rule won't be published in the Federal Register until Wednesday, showing up in the official record a little over three months after it was first unveiled.

The rule, which would set new source performance standards for yet-to-be-constructed power plants is one of the central pillars of the president's climate-change agenda, second in importance only to an agency rulemaking for existing plants due out next summer.

Publication of the rule in the Federal Register is significant because it triggers the start of a 60-day public comment period. The agency will also hold a public hearing on the rule later this month in Washington.

Even though the rule has yet to be finalized, it has already proven extremely controversial. Environmental advocates have hailed it as a way forward on combating climate change, while industry groups say it will deal a deadly blow to the U.S. coal industry.

Laura Sheehan, senior vice president of communications for the coal-industry group, the American Coalition for Clean Coal Electricity, slammed the rule ahead of its publication on Tuesday.

"EPA's New Source Performance Standards are yet another example of bad energy policy from the Obama White House," she said, adding, "The rule's unachievable requirements will take reliable, affordable coal-fueled electricity out of our future energy equation."

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